The present invention relates to coating apparatuses and methods of applying coatings.
Coatings are utilized in a variety of settings to provide a variety of benefits. For example, modern gas turbine engines can include thermal barrier coatings (TBCs), environmental coatings, etc. to help promote efficient and reliable operation. Application of coatings can involve a variety of different application methods, such as electron beam physical vapor deposition (EB-PVD). When TBCs are applied to gas turbine engine components, such as blades and vanes, using EB-PVD, the components being coated are first preheated and oxidized and then moved to a process chamber for deposition of the coating material. During the pre-heating stage, the components to be coated are in a pressure-controlled environment and an oxygen-containing gas may be present.
A significant problem with known pre-heating apparatus for use with EB-PVD is the degradation of heating elements. Known pre-heating chambers rely on graphite-based materials to protect against heat loss and as a material from which heating elements themselves are constructed. Such graphite components are life-limited because oxygen present in the pre-heating apparatus reacts with the graphite causing gradual erosion and degradation of both thermal insulation properties and heating capability of the graphite components. Degradation of pre-heater components requires eventual replacement of those components, which is burdensome and causes undesired expense. An additional problem associated with graphite components is the risk for detrimental and undesirable transfer of carbon to the components being pre-heated for coating, through a series of chemical reactions involving O2, CO2, CO and C (graphite). The transfer of carbon to the components to be coated poses a risk of poor or undesired coating properties.